Invoice Summary line items for recipient &1 and payer &2 exist

What causes this issue?

Open line items for invoice summary recipient &V1& and invoice summary
payer &V2& exist. The corresponding invoice is not created yet.
The creation of the invoice might not be possible if the invoice summary
role assignment has been changed.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Change the invoice summary role assignment only if the monthly invoices
and payer invoices are created with transaction ISJP_CR.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.